Field of the Invention
The present invention relates to a sheet conveyance apparatus and an image forming apparatus including the sheet conveyance apparatus.
Description of the Related Art
Japanese Patent Application Laid-Open No. 2005-162426 discusses an apparatus that detects overlapping (double feed) of sheets during conveyance by an ultrasonic sensor. Japanese Patent No. 4410212 discusses an apparatus including a double feed detecting sensor that detects double feed of sheets and configured to detect double feed of sheets by the double feed detecting sensor in an area which is adjacent to a nipping location of sheet and in which the amplitude of sheet is restricted.
When double feed of sheets is detected using an ultrasonic sensor, it is desirable that the orientation of sheets is stable in order to reduce variations of detected data by the ultrasonic sensor. Sheet grammage is sometimes determined using an ultrasonic sensor and also in this case, it is desirable that the orientation of sheets is stable.
In the apparatus, like the one discussed in Japanese Patent No. 4410212, a double feed detecting sensor is arranged in an area adjacent to a nipping location of sheet, the displacement width of sheet is restricted and the orientation of sheet is stabilized, but the following problem arises: an air layer between doubly-fed sheets is reduced and attenuation of an ultrasonic wave by the air layer is reduced. Then, depending on the type of sheet, it becomes difficult to determine double feed using the attenuation of an ultrasonic wave by the air layer. If the attenuation of an ultrasonic wave by the air layer is reduced, the precision of detection of sheet grammage is also deteriorated.